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Date:         Wed, 26 Nov 1997 10:45:29 -0800
Reply-To:     Andrew Mera <am1973@MONIKA.DS.BOEING.COM>
Sender:       Vanagon mailing list <Vanagon@Gerry.SDSC.EDU>
From:         Andrew Mera <am1973@MONIKA.DS.BOEING.COM>
Subject:      EV brake vibrations, summary
Comments: cc: tabrun@classic.msn.com, cjquijano@compuserve.com,
          rickgo@halcyon.com, spencervw@aol.com, schermer@bvsd.k12.co.us,
          kdf_cars@mylink.net, termite@rocketmail.com,
          throttle@alpha.alphalink.com.aualink

e diagnosis, and the fix. I am also attaching relevant comments.

My 95 Eurobago has developed a pulsation of the brake pedal when applied lightly at speeds above 50 mph; feels like something is out of balance up front between the pedal and the road: rotors, pads, hydraulics, tires, whatever. I don't have ABS (anti-lock break system), rather dual diagonal braking circuits with load sensitive braking. I have 2 disk in the front, 2 drums in the back.

Upon harder brake application at high speed, or below 40 mph, the vibration goes away. I consider it a safety issue because in an emergency situation I'd hesitate to slam on the brakes.

My original Goodyear tires have 20k miles, cann't see any uneven wear. VW first replaced the front brake rotors under warranty; this didn't change anything. I took it back and persisted until they agreed that there is still a problem: it turned out that the rear drum was uneven and somewhat warped (jim catterson gets the top prize for the best diagnosis). The 20 cps resonance, higher frequency than the tire rotation, can probably be explained by the break shoe vibrating against the uneven drum. Suspected cause of wear: during extended downhill breaking the drums get overheated, then one stops and applies the handbrakes, the drums may warp; prevention suggested: letting the brakes cool for one minute first.

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from Tom Brunson <TABRUN@classic.msn.com>

I notice the same thing on my '97 - apparently related to the ABS - but it shouldn't be there. The ABS functions when it senses a difference in wheel speed, and rapidly pulses the brake pressure to even things out and keep a wheel from skidding. I'd guess the sensors are not functioning just right - sensing a difference in rotation that isn't there. (I notice it most in very LIGHT braking; while ABS should only kick in with hard stops.). My '93 EV also has ABS and did not have this symptom.

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from Christopher Quijano <cjquijano@compuserve.com>

Is the vibration similar to what you feel when the ABS system kicks in? It has a very noticable feedback to the foot.

---------------------------------------------------------------------------

from Spencer SPENCERVW@aol.com

My 93GL has a kind of "GRUMBLING" noise when hard breaking from high speed. I have replaced the pads and rotors but the noise is still there. IT DOESN'T SEEM TO AFFECT BRAKING.

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from Rick Gordon <rickgo@halcyon.com>

I've had interesting vibrations in the Volvo tires when one of the steel belts broke. I couldn't even see it until a mechanic showed it to me - just a slight bump - even then I was skeptical but replacing the tire fixed the problem. Although I don't think this is your problem I just thought I'd point out how subtle the irregularity in the tire can be to cause significant vibrations!

(Actually this could be the problem - if it were in the rear tires you wouldn't feel it in the steering wheel - but when the pads made contact with the rotors there *might* be a vibration which pushes hydraulic fluid back - then again there are a lot of valves between the pedal and the pads so I'm just guessing.

Other thoughts: brake pads wearing down. Some pads I think have a material that's designed to make noise/vibration before you get to the metal. If your tires have 20K miles then your brakes do too? There's a lot of mass to be stopping in that van and they may wear faster than normal. But you replaced the front rotors? That almost implies the pads were wore down. What about the rears?

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from Richard M. Schermerhorn <schermer@bvsd.k12.co.us>

I have a '95 Eurobago and have experienced the same type of problem on an intermittent basis. Anyone else?

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from Rick Sherrod (kdf_cars@MYLINK.NET)

I have seen many problems with ABS systems caused by Ferrous particles stuck to the magnetic ABS sensor at the wheel. If too much ferrous material is present the sensor will not read the serrations on the wheel or CV joint and will tell The ABS computer that that wheel is locked and must be pulsed (what you are feeling through the pedal). The ferrous material comes from normal wear of the rotors. I always clean the sensors off with compressed air when I have the wheels off of an ABS equipped vehicle in my shop and this avoids vague ABS malfunctions.

---------------------------------

from jim catterson (termite@ROCKETMAIL.COM), 93 ev gl

The vibration problem, if it is not a severe abs pulse-like problem, is probably just warped rotors as someone previously posted. Have had this problem w/ everything from Volvos to Explorers if either the prior brake job didn't include cutting the rotors (if they can be cut) or the rotors need replacing. My ev w/52k also vibrates (non abs) and the prior owner just replaced the pads. I will try cutting then move on to replacing w/ cross drilled rotors.

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from Reece Isaac <throttle@alpha.alphalink.com.au>

Can't say that I've had that problem with my 96 T4 diesel (it's got just over 36000km. on it now) but I have had the Brake servo fail twice and a vacuum pump fail in the first 15 months I've owned it. Luckily it was covered under warranty. It seems that the pump was allowing oil up into the serve which caused the failures. Had an unusually high oil consumption rate also till the pump was replaced. Is yours 2 discs and 2 drums or 4 discs? If it's the former have you had the drums checked?


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